Describe a process that seems slow or delayed as "retarded." For example, if a person sprained her ankle, you could say that her walking was retarded. This means that her walking was delayed or held back by something.
Use the term to refer to an instance in which a person's academic progress is delayed. "Retard," as a verb, has two meanings. The first refers to a generally delayed process, and the other refers to an institution holding a student back academically. To "retard" a person's education would be, for example, to retain a student at a certain level for more than one year, or assign him or her a failing grade in a class.
Determine whether or not the use of the word "retard" or "retarded" is accurate. You may be able to find a word that is closer to your intended meaning. If you're using the words "retard" or "retarded" to describe something that is crazy, silly, ludicrous or nonsensical, then you are misusing the word. Find an adjective that is more appropriate.